1. Field of the Invention
The present invention relates generally to coring assemblies and, more particularly, to apparatus and methods for facilitating inner core barrel latching in coring assemblies.
2. Description of the Background
Conventional coring tools for obtaining core samples from a borehole comprise a tubular housing attached at one end to a special bit often referred to as a core head, and at the other end to a drill string extending through the borehole to the surface. The tubular housing includes an inner and outer barrel with a space between. During normal drilling the drilling fluid may flow through the interior of the inner barrel. When a core sample is required, the flow passageway is blocked, often by dropping a ball from the earth's surface, thus diverting the flow into the space between the inner and outer barrel and down through the bit. The absence of flow in the inner barrel allows the earth formation to enter and fill the barrel, which is then subsequently recovered as a core.
Wire-line retrievable coring tools are often used to allow multiple core samples to be taken without the need to remove the drill string. Retrieval of continuous samples allows for enhanced core analysis, including mechanical rock properties, mineralogy and lithology (including petrography), rock fabric (including grain size), stratigraphic correlation, and paleontology. Preferably all zones of interest are captured to enhance the entire hydrocarbon recovery process from geologic interpretation through reservoir management. As well, enhanced analysis of the above-reservoir formations allows the operator to better address problems such as well-bore stability and fluid/formation capability.
Wire-line retrievable coring tools typically have latching mechanisms which hold the inner barrel in place at a fixed axial orientation with respect to the outer barrel. While the inner barrel must be held in a fixed position axially, it must also be free to rotate with respect to the outer barrel to avoid twisting the core. The latch mechanism must reliably latch the inner barrel in place when the inner barrel is lowered into position and it must reliably unlatch the inner barrel to allow retrieval of the core sample via wireline.
Latching problems may prevent the coring tool from obtaining a core sample thus costing rig time and loss of information. For instance, the latching mechanism may fail to latch the inner barrel in position prior to taking a core sample so that the core never enters the inner core barrel. Such a failure may not be readily discernable from the surface. Thus, the failure to latch may result in a failure to obtain a desired core sample from a potentially producing zone of interest in the formation. After drilling through the zone, the core sample may be more difficult to obtain and may be more contaminated with drilling fluid than if the sample was obtained in the first place without failure of the latch.
While the most common latching failure is that of the inner barrel failing to latch to the outer barrel, it is also possible to have an unlatching failure where the coring tool fails to unlatch after the surface operator believes the inner core sample has been taken. Such a failure results in the need to pull the drill string with the attendant cost in time. As well, latching mechanisms require additional cost for manufacturing as well as ongoing cost of maintenance.
Consequently, there remains a need for a coring assembly that offers dependable operation at reduced levels of capital investment. Those skilled in the art have long sought and will appreciate the present invention which provides solutions to these and other problems.